The present invention relates to an integrated circuit voltage comparator and more particularly to a voltage comparator capable of common mode comparisons at both extremes of power supply voltages. The present invention finds particular utility utility where a high level of precision is required.
Circuits for making voltage comparisons are well known. Generally, two independent differential amplifiers or comparator are required--one operational at signal levels near one extreme of the power supply and the other operational at signal levels near the other extreme of the power supply. Each of these two independent comparator feeds a high impedance load from which an output signal can be taken, and the two output signals are combined to provide a single output signal from the comparator circuit. One circuit of this type is disclosed in the Hoover U.S. Pat. No. 4,333,058 dated Jan. 1, 1982.
Known comparators thus require two independent circuits with all of the circuit complexity and expense attendant thereto. In addition, known comparators do not operate in a wide common mode range, i.e., they are not generally functional over the entire voltage range of the power supply. Finally, known comparators lack the precision desired for many applications, particularly where the range of comparison is large.
Accordingly, it is an object of the present invention to provide a novel comparator and method for rail to rail voltage comparison.
It is another object of the present invention to provide a novel comparator and method in which high precision is obtained over substantially the full range of power supply voltage.
It is yet another object of the present invention to provide a novel comparator and method in which the number of circuit elements is significantly reduced by sharing among the positive and negative channels.
It is still another object of the present invention to provide a novel comparator and method in which the positive and negative signal paths share a common current source and load throughout the entire common mode range from the positive to the negative power supply rails.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.